JPH08194364A - Image forming device - Google Patents

Abstract

PURPOSE: To make the preventing of the contamination of and the long life of an image carrier compatible by changing removing amounts of the surface of the image carrier in high temp. and high humidity environments and in low temp. and low humudity environments. CONSTITUTION: In an image forming device having a elecrifier 2 performing electrification on an image carrier 1 being a body to be elecrified by impressing a voltage in which a AC component and a DC component arc superposed on an electrifying member and a detection means 8 detecting either the temp. or the humidity or both of them in a main body, the preventing of the contamination of and the long life of the image carrier are made to be compatible by eliminating the comtaminating of the image carrier while sufficiently performing the grinding of the image carrier in the high temp. and high humidity environments and by suppressing the removing amount of the image carrier in the low temp. and low humidity environments while changing (9) the frequency of the AC component of the voltage impressing on the electrifier according to the detection results of the detection means 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a laser beam printer or an electrophotographic apparatus.

[0002]

2. Description of the Related Art FIG. 2 is a diagram showing a conventional image forming apparatus. A description will be given below with reference to the drawings. The photosensitive drum 1, which is an image bearing member, has an organic photosensitive member (OP
C) is applied to form a photoconductor, which is driven in the direction of the arrow in the drawing by a driving unit (not shown) to be uniformly charged to a predetermined potential by the roller charger 2.

The roller charger 2 has the advantage that ozone, which is harmful to the human body, is extremely less than the conventional corona charger, and has been put into practical use in recent years.
DC voltage controlled to a constant voltage of V and frequency of 1000
By applying a voltage on which an AC voltage having a peak-to-peak voltage (Vpp) of 2000 V at Hz is applied, the photosensitive drum 1 is uniformly charged to approximately -700 V.

Here, it is necessary to set the frequency of the AC voltage to a frequency that prevents a minute potential unevenness due to AC charging and a density unevenness (moiré) caused by interference of an image pattern. It is determined by the size of 1 dot.

For example, in a 600 dpi image forming apparatus, a halftone image pattern consisting of a continuous 1-dot horizontal line and 3-dot horizontal line is 25.4 ÷ 60.
It has a periodicity of 0 × (1 + 3) = 0.1693,
Process speed is 100 mm / sec. Then 100
÷ Moire occurs at a charging frequency near 0.1693 = 590.6 Hz.

From the results of the experiments conducted by the present inventors, the occurrence of moire becomes remarkable within ± 10% around the time when the repeating width of the image pattern and the period of the potential unevenness of charging coincide. In order to suppress the occurrence of moire, it is necessary to avoid the frequencies and set the charging frequency, and in the present image forming apparatus, approximately 1000 Hz is preferable.

Next, laser exposure L according to the image pattern
Is irradiated onto the photosensitive drum 1, and a latent image is formed on the photosensitive drum 1. Further, the photosensitive drum 1 advances in the direction of the arrow and is visualized as a toner image by the developing device 3. The developed toner image is transferred onto the transfer paper 7 by the transfer charger 5.
Further, the transfer paper 7 is fused and fixed by a conventionally known heating and pressure fixing device 6 to obtain an image. The transfer residual toner on the photosensitive drum 1 is cleaned by a cleaning device 4 of a known blade means.

In the image forming apparatus as described above,
The photoconductor is not only soiled by the transfer residual toner, but also is gradually contaminated by the components of the transfer material and the discharge products at the time of charging by repeated use. As described above, when the photoconductor is contaminated, the resistance of the surface is lowered and the electrostatic latent image is disturbed, or the toner and its components are fused to the photoconductor surface, and the image is remarkably damaged. Become. In recent years, image forming apparatuses such as laser printers are strongly demanded to have high image quality, and in terms of resolution, 600 dpi or 800 dpi,
In addition, it is progressing toward multi-valued image processing in which image processing such as PWM (pulse width modulation) is performed, and even a slight contamination of the photoconductor appears on the image.

Therefore, in the conventional image forming apparatus, a good image is maintained by positively polishing the surface of the photosensitive drum with a cleaning blade to refresh the surface. As a result, the thickness of the photosensitive layer is durable. Decreases with The photoconductor acts as a capacitor in a dark portion (a portion not exposed to light), and when an electric charge is applied, it is retained and appears as a surface potential.

However, when the film thickness of the photoconductor is too thin, the amount of electric charge provided by the charger is limited, so that the surface potential is lowered, and the film of the photoconductor has some defects. Therefore, the charge may locally escape, which may lead to poor charging. Therefore, in order to maintain a good image, there is a minimum required film thickness. In the OPC used in the present invention, the minimum thickness of the uppermost charge transport layer (CT layer) is 10 μm, and the photoreceptor has a CT layer thickness of 1 μm.
When it reaches 0 μm, the life is reached.

[0011]

However, as a result of repeated studies by the present applicant, the following problems have occurred.

The environment in which the image forming apparatus is used varies from high temperature and high humidity to low temperature and low humidity, and the amount of abrasion of the photoconductor per number of sheets used is different between the high temperature and high humidity environment and the low temperature and low humidity environment. As a result of the experiment by the applicant, a low temperature and low humidity environment (1
The amount of photoconductor abrasion at 5 ° C, 10%)
It was 1.5 μm per 00 sheets, but 1.0 μm in a high temperature and high humidity environment (30 ° C., 80%).

On the other hand, the contamination of the photoreceptor such as toner fusion occurs remarkably in a high temperature and high humidity environment, and with the scraped amount, the fusion was not sufficiently polished to obtain a good image.

In addition to the conventional method for increasing the amount of abrasion of the photoconductor, the contact pressure of the cleaning blade is increased or an abrasive is externally added to the developer to enhance the polishing effect. However, in that case, the abrasion amount of the photoconductor also increases in a low temperature and low humidity environment, and the life of the cartridge is shortened.

For example, in an experiment conducted by the applicant of the present invention, the abrasion amount of the photosensitive member was 10 when the contact pressure of the cleaning blade was increased until the toner fusion was sufficiently polished under a high temperature and high humidity environment.
The number of sheets per sheet was 1.2 μm, and the abrasion amount of the photoconductor under the low temperature and low humidity environment was 1.8 μm. When the initial film thickness of the uppermost layer of the photoconductor is set to 20 μm, the film thickness reaches its life under low temperature and low humidity environment.
The number of printable sheets (up to μm) decreases from about 6500 sheets to about 5500 sheets.

The present invention is proposed in view of the above-mentioned problems, and an object thereof is to form an image without shortening the life of the photoconductor and causing no photoconductor contamination under a high temperature and high humidity environment. It is to provide a device.

[0017]

According to the first invention of this application, the frequency of the bias applied to the charging roller is changed according to the operating environment of the apparatus to prevent the contamination of the photoconductor and the long life of the photoconductor. compatible.

According to the second aspect of the invention, depending on the environment in which the device is used,
By changing the number of rotations after the photoconductor after printing,
Achieves both prevention of contamination of the photoconductor and long life of the photoconductor.

[0019]

【Example】

(First Embodiment) In the present embodiment, attention is paid to the fact that when the frequency of the charging bias is increased, the abrasion amount of the photoconductor is increased accordingly. Therefore, the frequency of the charging bias is increased in a high temperature and high humidity environment, and It positively polishes to prevent drum contamination, and at the same time, realizes a long life of the photoconductor even in a low temperature and low humidity environment.

FIG. 1 shows a sectional view of an image forming apparatus according to the present invention. It should be noted that members having the same configurations and functions as those of the conventional image forming apparatus shown in FIG. 2 are denoted by the same reference numerals, and description thereof will be appropriately omitted.

A photosensitive drum 1 as an image bearing member is arranged substantially in the center of the apparatus main body. The photosensitive drum 1 is rotatably supported, and a roller charging charger 2, a developing device 3, a transfer charger 5, a cleaning device 4, and the like are sequentially arranged around the photosensitive drum 1 in the rotation direction (direction of arrow R1). It is arranged. Further, a fixing device 6 is arranged below the main body of the apparatus.

First, the environment sensor 8 measures the temperature and humidity of the environment in which the device is used. The main body CPU 9 calculates the absolute water content of the environment from the temperature and humidity measured by the environment sensor 8 and determines the frequency of the charging bias. In this embodiment, the calculated environmental moisture content is 9 g / kg (20
(Corresponding to a normal temperature and humidity environment of 60 ° C. and 60%), the charging bias frequency is set to 1000 Hz, and when the environmental water content exceeds 9 g / kg, the charging bias frequency is set to 20.
Set to 00Hz. The absolute water content referred to here means the water content per 1 kg of dry air.

Charging frequency = 2 under high temperature and high humidity environment
Since 000 Hz is a value twice the conventional frequency of 1000 Hz, moire does not occur.

As a result of the experiment, in this embodiment, the amount of abrasion of the photoconductor under high temperature and high humidity environment was 1.4 μm per 1000 sheets, the photoconductor was sufficiently polished, and the photoconductor was not contaminated. In addition, the amount of photoconductor abrasion under the low temperature and low humidity environment does not change as before, and the initial film thickness of the photoconductor uppermost layer is 20%.
In case of μm, until the film thickness reaches the end of life (the film thickness is 10
The number of printable sheets (up to μm) was about 6500.

As described above, according to the present embodiment, by changing the frequency of the bias applied to the charging roller in accordance with the environment in which the apparatus is used, it is possible to prevent contamination of the photoconductor and extend the life of the photoconductor. .

(Second Embodiment) In this embodiment, the number of rotations of the photosensitive member after printing is changed in accordance with the operating environment of the apparatus to prevent the contamination of the photosensitive member and extend the life of the photosensitive member.

Similar to the first embodiment, the environment sensor 8 measures the temperature and humidity of the environment in which the device is used. Body CP
U9 is the temperature and humidity measured by the environment sensor 8,
The absolute water content of the environment is calculated, and the number of post-rotation of the photoconductor after printing is determined according to the calculated value. Conventionally, the post-rotation of the photoconductor after printing is performed twice for the purpose of cleaning the transfer residual toner and removing the charge of the photoconductor. In this example, the calculated environmental moisture content was 9 g / kg (20 ° C., 6
(Corresponding to 0% room temperature and normal humidity environment) or less, the number of rotations after photoconductor is set to 2 rotations, and when the environmental water content exceeds 9g / kg, the number of rotations after photoconductor is increased to 4 rotations. Improves the body polishing effect and prevents photoreceptor contamination.

As a result of the experiment, in the present embodiment, the amount of abrasion of the photoconductor in a high temperature and high humidity environment was 1.3 μm per 1000 sheets, the photoconductor was sufficiently polished, and the photoconductor was not contaminated. In addition, the amount of photoconductor abrasion under the low temperature and low humidity environment does not change as before, and the initial film thickness of the photoconductor uppermost layer is 20%.
In case of μm, until the film thickness reaches the end of life (the film thickness is 10
The number of printable sheets (up to μm) was about 6500.

As described above, according to the present embodiment, it is possible to prevent contamination of the photoconductor and extend the life of the photoconductor by changing the number of rotations of the photoconductor after printing according to the operating environment of the apparatus. It was

[0030]

As described above, according to the first aspect of the present application, the frequency of the bias applied to the charging roller is changed according to the usage environment of the apparatus to prevent contamination of the photoconductor and increase the length of the photoconductor. It has become possible to achieve both lifespan.

In the second aspect of the invention, depending on the operating environment of the device,
By changing the number of rotations after the photoconductor after printing,
It has become possible to both prevent contamination of the photoconductor and extend the life of the photoconductor.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a diagram showing an example of a conventional image forming apparatus.

[Explanation of symbols]

1 ... Photosensitive drum 2 ... Roller charging device 3 ... Developing device 4 ... Cleaning device 5 ... Transfer device 6 ... Fixing device 7 ... Transfer paper 8 ... Environmental sensor 9 ... Main body CPU L ... Laser exposure

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akihiko Uchiyama 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (3)

[Claims] 1. A charging device for applying a voltage having an alternating current component and a direct current component superposed to a charging member to charge an image carrier, which is a member to be charged, and either one or both of temperature and humidity inside the main body. An image forming apparatus having a detecting means for detecting the above, wherein the frequency of the AC component of the voltage applied to the charger is changed according to the detection result of the detecting means. 2. The image forming apparatus according to claim 1, wherein the charging member is in contact with the image carrier. 3. An image forming apparatus having a photoconductor, which is an image bearing member, and a detection means for detecting one or both of temperature and humidity inside the main body, and printing is performed according to the detection result of the detection means. An image forming apparatus, characterized in that the number of post rotations of the photoconductor is changed.